In co-pending co-owned application Ser. No. 795,405, filed May 9, 1977, there is disclosed a modular rod lens assembly particularly suited for use in endoscopes. The assembly takes the form of a thin metal outer tube containing a series of small rod lens modules dimensioned and arranged to transmit an optical image from one end of the assembly to the other. Enclosed within the same tube is a bundle of light-transmitting glass fibers. In use, the glass fiber bundle transmits light through the tube to illuminate that portion of the body undergoing examination, the lens system then returning the image of the illuminated area to the eye of the surgeon or other person utilizing the instrument.
Such an assembly must be manufactured to extremely high standards of precision and cleanliness if the assembly is to perform its microscope functions efficiently and effectively. Because of the frangibility of glass fibers, difficulties have been encountered in the past in potting such fibers to form a bundle of precise dimensions without damaging the fibers and producing debris either from the fibers themselves or from the potting material. Also, because of the hardness of such fibers, contact between the bundle and the surfaces of other elements, such as the inside surface of the endoscope tube or barrel, may result in abrasion, damage, and the generation of particulate matter. Should any such particulate matter enter the spaces between the opposing end faces of successive rod lenses, the optical performance of the microscope might be seriously impaired, particularly because in a rod lens system, unlike camera systems, the faces of the lenses often lie in or near the image planes. Therefore, any particulate matter on the end faces of the rod lenses might appear in the field of view when the completed assembly is put to use.
An important aspect of this invention lies in the discovery that the difficulties of fabricating a potted glass fiber bundle, as well as the problems arising in the assembly and use of such a bundle in conjunction with the other elements of an endoscope, may be greatly reduced if the bundle is cast or molded between a pair of films which not only simplify removal of the bundle from the mold but which become part of the final light guide to reduce friction, improve abrasion resistance, and virtually eliminate all problems of shedding and debris development. Specifically, the films protect the glass fibers against damage from other elements, protect such other elements (such as the rod lens modules and the endoscope barrel) against abrasive contact by such fibers, reduce frictional resistance when the light guide and other elements are assembled to form the endoscope, and virtually eliminate shedding and debris formation which might impair the effectiveness of the final instrument.
Briefly, the method comprises the steps of lining the cavity of a mold with a thin flexible film of plastic or other suitable material, introducing a multiplicity of generally parallel glass fibers and a liquid potting resin into the lined cavity, covering the exposed fibers and resin with a second film, then introducing an insert element into the cavity to reform the assemblage of films, resin, and fibers into a predetermined cross-sectional configuration, and then allowing the potting compound to pass into its hardened state to form a dimensionally stable structure in which the films are secured in place to form a protective sheath.
The completed light guide is ideally crescent-shaped in cross section although other configurations might be suitable. In the final endoscope assembly, the convex curvature of the crescent-shaped light guide engages the inside surface of the endoscope barrel while the concave curvature contacts the rod lens modules. During assembly of such components, the protective films provide smooth abrasion-resistant non-shedding surfaces, thereby eliminating or greatly reducing the possibility of damage to the waveguide itself or to the other elements of the instrument. Furthermore, where the instrument is capable of limited flexure, the abrasion-resistant cladding continues to perform its important functions in protecting the parts and preventing debris formation during such occasional flexure and throughout the useful life of the instrument.
Other advantages and objects of the invention will become apparent from the specification and drawings.